Communication: Probing non-equilibrium vibrational relaxation pathways of highly excited C≡N stretching modes following ultrafast back-electron transfer

Fifth-order nonlinear visible-infrared spectroscopy is used to probe coherent and incoherent vibrational energy relaxation dynamics of highly excited vibrational modes indirectly populated via ultrafast photoinduced back-electron transfer in a trinuclear cyano-bridged mixed-valence complex. The flow of excess energy deposited into four C≡N stretching (ν(CN)) modes of the molecule is monitored by performing an IR pump-probe experiment as a function of the photochemical reaction (τ(vis)). Our results provide experimental evidence that the nuclear motions of the molecule are both coherently and incoherently coupled to the electronic charge transfer process. We observe that intramolecular vibrational relaxation dynamics among the highly excited ν(CN) modes change significantly en route to equilibrium. The experiment also measures a 7 cm(-1) shift in the frequency of a ～57 cm(-1) oscillation reflecting a modulation of the coupling between the probed high-frequency ν(CN) modes for τ(vis) < 500 fs.     

A mild and efficient method for halogenation of 3,5-dimethyl pyrazoles by ultrasound irradiation using N-halosuccinimides

The 4-halo-3,5-dimethyl pyrazoles have been synthetisized in good yields in short reaction times in the absence of a catalyst by reaction of 3,5-dimethyl pyrazoles with N-halosuccinimides (NBS, NCS and NIS) under ultrasound irradiation. Finally, the halogenation of pyrazoles with Br₂, ICl and I₂ was showed in similar conditions.     

Nafion/tetraruthenated porphyrin glassy carbon-modified electrode: characterization and voltammetric studies of sulfite oxidation in water–ethanol solutions

In this work, the modification of a glassy carbon electrode with tetraruthenated porphyrins electrostatically assembled onto a Nafion film, previously adsorbed on the electrode surface, is reported. This modified electrode was characterized by scanning electron microscopy–energy-dispersive X-ray, Raman spectroscopy, UV-Vis spectroelectrochemistry, and cyclic voltammetry. The Nafion film onto the glassy carbon electrode shows a smooth disposition; when the tetraruthenated porphyrin is incorporated on the Nafion film, the complex is adsorbed in a homogeneous way. The modified electrode catalyzes HSO₃⁻ oxidation in water–ethanol solutions and shows an enhanced stability compared with the electrode modified with the dip coating method. Rotating disk electrode experiments showed a kinetic limitation to the electron transfer controlled by charge propagation in the film. I/E curves show a Tafel slope of 120 mV/decade corresponding to a first electron-transfer reaction, depending on the potential, as the determining step. Spectroelectrochemical experiments demonstrated that Ru(II) is the active site for the electrocatalysis.     

Partial filling multiple injection affinity capillary electrophoresis (PFMIACE) to estimate binding constants of receptors to ligands

Partial filling multiple injection affinity capillary electrophoresis (PFMIACE) is used to determine binding constants between vancomycin (Van) from Streptomyces orientalis, teicoplanin (Teic) from Actinoplanes teicomyceticus and ristocetin (Rist) from Nocardia lurida to d-Ala-d-Ala terminus peptides and carbonic anhydrase B (CAB, E.C.4.2.1.1) to arylsulfonamides. Two variations of PFMIACE are described herein. In the first technique, the capillary is partially filled with ligand at increasing concentrations, a non-interacting standard, three or four separate plugs of receptor each separated by small plugs of buffer, a plug containing a second non-interacting standard, and then electrophoresed in buffer. Upon continued electrophoresis, equilibrium is established between the ligand and receptors causing a shift in the migration time of the receptors with respect to the non-interacting standards. This change in migration time is utilized for estimating multiple binding constants (K_b) for the same interaction. In the second technique, separate plugs of sample containing non-interacting standards, peptide one, buffer, and peptide two, were injected into the capillary column. The capillary is partially filled with a series of buffers containing an antibiotic at increasing concentrations and electrophoresed. Peptides migrate through the column at similar electrophoretic mobilities since their charge-to-mass ratios are approximately the same but remain as distinct zones due to the buffer plug between peptides. Upon electrophoresis, the plug of antibiotic flows into the peptide plugs affecting a shift in the migration time of the peptides with respect to the non-interacting standards occurs due to formation of the of the antibiotic-peptide complex. The shift in the migration time of the peptides upon binding to the antibiotic is used for the Scatchard analysis and measurement of a K_b. The PFMIACE technique expands the functionality and potential of ACE as an analytical tool to examine receptor-ligand interactions. In PFMIACE, a smaller amount of sample is required in the assay compared to both conventional ACE and MIACE. Furthermore, a wide array of data is obtained from a single experiment, thus, expediting the assay of biological species.     

Rearrangement of spiro-benzimidazolines: preparation of N-alkenyl- and N-alkyl-benzimidazol-2-ones

A synthetically useful protocol has been developed for the preparation of highly functionalized N-alkenyl-benzimidazol-2-ones. Reaction of commercially available o-phenylenediamines with variously substituted cyclic ketones provides spiro-benzimidazolines. Treatment of these spiro-benzimidazolines with triphosgene in the presence of potassium carbonate results in rapid rearrangement and formation of N-alkenyl-benzimidazol-2-ones in modest to excellent yield for the two-step sequence. Extension of this methodology toward the preparation of a μ opiate receptor antagonist and droperidol, a potent antiemetic and antipsychotic agent, currently a marketed pharmaceutical is also described. Upon treatment of spiro-benzimidazolines with triphosgene in the presence of sodium triacetoxyborohydride, N-alkyl-benzimidazol-2-ones were formed.     

From anisole to 1,2,4,5‐tetramethoxybenzene: Theoretical study of the factors that determine the conformation of methoxy groups on a benzene ring

Unhindered ortho‐dimethoxy‐substituted phenyl rings often display a coplanar conformation. A theoretical study of a series of methoxybenzenes consisting of methoxybenzene (anisole), the three dimethoxybenzenes, and 1,2,4,5‐tetramethoxybenzene, at the DFT/B3LYP/6‐311++G** level of theory, allows us to identify the factors influencing the conformational preference and attribute the coplanarity of such methoxy groups to mesomeric effects. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Capillary zone electrophoresis of cationic and anionic drugs in methanol

The actual mobilities and dissociation constants of acidic and basic pharmaceuticals were determined in methanol. Actual mobilities were derived from the dependence of the effective mobilities of the analytes on the pH of the methanolic background electrolyte solution (pH(MeOH)). The pKa values of the pharmaceuticals in methanol (pK(a,MeOH)) were calculated by non-linear curve fitting to the measured mobility values. It was found that the shift in pKa value (when compounds were transferred from water to methanol) increased with the acidity of the analyte. The average pKa shift for compounds exhibiting acidic properties in water was ca. 5.5 units, and the shift for basic compounds about 2 units. As was shown for a mixture of beta-blockers, the calculated actual mobilities and pKa values can be utilised in the optimisation of pH conditions for separation. The practical value of the method was illustrated by the analysis of urine samples.     

Components of Banisteriopsis caapi,a Plant Used in the Preparation of the Psychoactive Ayahuasca,Induce Anti-Inflammatory Effects in Microglial Cells

Banisteriopsis caapi is used to prepare the psychoactive beverage ayahuasca, and both have therapeutic potential for the treatment of many central nervous system (CNS) conditions. This study aimed to isolate new bioactive compounds from B. caapi extract and evaluate their biological activity, and that of the known β-carboline components of the plant (harmine, harmaline, and tetrahydroharmine), in BV-2 microglial cells, the in vivo activation of which is implicated in the physiopathology of CNS disorders. B. caapi extract was fractionated using semipreparative liquid chromatography (HPLC-DAD) and the exact masses ([M + H]⁺ m/z) of the compounds in the 5 isolated fractions were determined by high-resolution LC-MS/MS: F1 (174.0918 and 233.1289), F2 (353.1722), F3 (304.3001), F4 (188.1081), and F5 (205.0785). Harmine (75.5–302 µM) significantly decreased cell viability after 2 h of treatment and increased the number of necrotic cells and production of reactive oxygen species at equal or lower concentrations after 24 h. F4 did not impact viability but was also cytotoxic after 24 h. Most treatments reduced proinflammatory cytokine production (IL-2, IL-6, IL-17, and/or TNF), especially harmaline and F5 at 2.5 µM and higher concentrations, tetrahydroharmine (9.3 µM and higher), and F5 (10.7 µM and higher). The results suggest that the compounds found in B. caapi extract have anti-inflammatory potential that could be explored for the development of treatments for neurodegenerative diseases.     

Electrochemical interfaces on chalcogenides: Some structural perspectives and synergistic effects of single-surface active sites

The use of single-atom metals (SAM) as catalysts of energy conversion reactions is a recent topic, which has gained popularity in the last two decades. Transition metal dichalcogenides emerged as important electrocatalysts since it was discovered that their chalcogenide edge sites are active towards the electrocatalytic hydrogen evolution reaction (HER) and could also serve as supports for other metals within the same applications. Currently, several groups have reported a novel metal?chalcogenide arrangement, with the possibility of isolating metals at specific sites on chalcogenides to enhance their properties resulting in a synergistic effect in which both chalcogenide and single-atom metal features are exploited, either as promoters or active sites. Theoretical studies have been the basis of these reports.